2What is a Volcano?Opening in the Earth (called a vent) that erupts gases, ash, and lava.Volcanic mountains result from the build-up of these materials.The steep walled depression that forms around a vent is called a crater.There are more than 600 currently active volcanoes.
6How do volcanoes form?Deep inside the Earth, heat and pressure cause rock to melt, forming magma.Because liquid rock (magma) is less dense than solid rock, it slowly rises, reaching the surface after many thousands of years.
7Where do volcanoes occur? Convergent boundariesDivergent boundariesHot spots
8Where do volcanoes occur? Divergent Plate BoundariesMagma flows onto the floor of the ocean at rifts (long, deep cracks in the ocean floor).Over time the cooled magma (igneous rock) can build up and form islands.Example:Iceland – Mid-Atlantic RiftSurtsey
11Where do volcanoes occur? Convergent BoundariesAs the subducting plate is heated by increasing temperature and pressure, it partially melts, forming magma that moves to the surface and usually causes violent eruptions.Examples:Mount St. Helen’s – Cascade Mountains
13Where do volcanoes occur? HotspotsAnomalies in the middle of plates where there are large amounts of heat.Hot spots are stationary whereas the plates above them continue to move.Examples:HawaiiYellowstone